In recent years, a technique referred to as OpenFlow has been proposed (see non patent literature (NPL) 1 and 2). OpenFlow recognizes communications as end-to-end flows and performs path control, failure recovery, load balancing, and optimization on a per-flow basis. An OpenFlow switch according to NPL 2 has a secure channel for communication with an OpenFlow controller and operates according to a flow table suitably added or rewritten by the OpenFlow controller. In a flow table, a set of the following three is defined for each flow: matching conditions (Match Fields) against which a packet header is matched; flow statistical information (Counters); and Instructions that define processing contents (see section “4.1 Flow Table” in NPL 2).
For example, when receiving a packet, the OpenFlow switch searches the flow table for an entry having a matching condition (see “4.3 Match Fields” in NPL 2) that matches header information of the incoming packet. If, as a result of the search, the OpenFlow switch finds an entry matching the incoming packet, the OpenFlow switch updates the flow statistical information (Counters) and processes the incoming packet based on a processing content (packet transmission from a specified port, flooding, drop, etc.) written in the Instructions field of the entry. If, as a result of the search, the OpenFlow switch does not find an entry matching the incoming packet, the OpenFlow switch transmits an entry setting request (Packet-In message) to the OpenFlow controller via the secure channel. Namely, the OpenFlow switch requests the OpenFlow controller to transmit control information for processing the incoming packet. The OpenFlow switch receives a flow entry defining a processing content and updates the flow table. In this way, by using an entry stored in the flow table as control information, the OpenFlow switch executes packet forwarding.
[NPL 1]
    Nick McKeown, and seven others, “OpenFlow: Enabling Innovation in Campus Networks,”[online], [searched on Jul. 13, 2012], Internet <URL:http://www.openflow.org/documents/openflow-wp-latest.pdf>[NPL 2]    “OpenFlow Switch Specification” Version 1.0.0 Implemented (Wire Protocol 0x01), [online], [searched on Jul. 13, 2012], Internet <URL:http://www.openflow.org/documents/openflow-spec-v1.0.0.pdf>